1. Field of the Invention
This invention relates to novolak type phenolic resins offering narrow molecular weight distributions, and methods of manufacturing thereof.
2. Prior Art
Conventionally, novolak type phenolic resins are obtained by making phenols react with aldehydes in the presence of an acidic catalyst, and are used in a wide variety of fields. However, with such conventional novolak type phenolic resins, the molecular weight distributions are wide, which results in such drawbacks as non-uniformity in resin curing time, and high viscosity in molten state.
To eliminate these problems, various methods have conventionally been used. For example, by making phenols react with aldehydes in the presence of an acidic catalyst in an organic solvent system which is composed of a good solvent and a poor one, a novolak resin offering a narrow molecular weight distribution has been obtained. A method of manufacturing novolak type phenolic resins by making phenols react with aldehydes in the presence of an acidic catalyst, and then treating the reaction product with a thin film evaporator has been proposed. As disclosed in Patent KOKAI (Laid-Open) No. 1-105243 and Patent KOKAI (Laid-Open) No. 6-41262, a method with which phenols are made to react with aldehydes in the presence of an acidic catalyst, and then the reaction product is washed with water or a mixed solvent of water and a good solvent for fractionation has been proposed.
However, with these methods of manufacturing, the processes are complicated, the yields of resin have been small, and the molecular weight distributions have not always been sufficiently narrow.